A Sigqueue is a signalling queue which maintains two data structures, and signals when the first of each are matching.
The Sigqueue depends on two data structures internally to track state. On the incoming side, there is a monotonically increasing linked list of IDers. On the waiting side, there is a heap of ready ids.
A Heap is a standard min-heap data structure, typed specifically to support the Sigqueue.
A LinkedList is a standard double-linked list, purpose built for sigqueue.
A Signal is a way to notify a consumer when a signal has been raised over channels.